swift234

Convert stdlib classes to use Builtin.isUnique.

Fixes <rdar://problem/18151694> Add Builtin.checkUnique to avoid lost Array copies

The isUniquelyReference APIs are now correct in the presence of full
inlining and ARC optimization. The ARC optimizer can't see into the
Builtin, which lowers to a special SIL instruction.

Swift SVN r27929